Framers are commonly used in networking systems. FIG. 1 illustrates an exemplary framer. A network line such as networking line 102 or networking line 103 in FIG. 1 couples a pair of networking systems (e.g., switches, routers, multiplexers, gateways, etc.) so that the pair of networking systems may communicate with one another. Examples of networking lines include fiber optic or copper cable. Note that for simplicity, physical layer devices (e.g., lasers/photo-detectors, line drivers, etc.) typically placed between the framer 101 and the networking lines are not shown in FIG. 1.
Frames (such as frames 108, 109, and 110) are used to organize the flow of information over a network line. In the case of SYNnchronous Optical Network (SONET) frames, each frame may be viewed as carrying “n” synchronous payloads envelopes (SPEs) of 810 bytes. Conceptually, as seen in FIG. 1, frame 108 carries SPEs 1111, 1112, 1113, . . . , 111n; frame 109 carries SPEs 1121, 1122, 1123, . . . , 112n; and frame 110 carries SPEs 1131, 1132, 1133, . . . , 113n. For simplicity, note that the overhead portions of each frame 108, 109, 110 are not shown.
For SONET frames, the time consumed by each frame (e.g., time T1 for frame 108, time T2 for frame 109, and time T3 for frame 110) corresponds to 125 μs regardless of the number of SPEs carried per frame (i.e., “n”). Furthermore, the number of SPEs carried per frame remains constant from frame to frame. Thus, the number of SPEs carried per frame is indicative of the network line speed.
For example, a SONET networking line having only one SPE per frame (i.e., n=1) corresponds to a line speed of 51.840 Mbs (i.e., 810 bytes every 125 μs). Similarly, a SONET networking line having three SPEs per frame (i.e., n=3) corresponds to a line speed of 155.52 Mbs (i.e., 2430 bytes every 125 μs), a SONET networking line having forty eight SPEs per frame (i.e., n=48) corresponds to a line speed of 2.488 Gb/s (i.e., 38880 bytes every 125 μs), etc. Note that if the applicable networking line is optical “OC” is typically used instead of “STS” (e.g., OC-3, OC-48, etc.).
One SPE per 125 μs is referred to as an STS-1 signal. Thus, a 51.840 Mbs SONET networking line carries a single STS-1 signal; a 155.52 Mbs SONET networking line carries three STS-1 signals; and a 2.488 Gb/s SONET networking line carries forty eight STS-1 signals. Typically, each STS-1 signal may be viewed as corresponding to the same SPE position across different frames. That is, a first STS-1 signal corresponds to SPEs 1111, 1121, and 1131; a second STS-1 signal corresponds to SPEs 1112, 1122, 1132; etc.
FIG. 1 shows a framer within a networking system 110 that acts as a node in a network. The framer 101 in FIG. 1 is one or more semiconductor chips that provide framing organization for a network line. For example, the exemplary framer 101 of FIG. 1: 1) formats STS-1 signals into frames that are transmitted on an outbound networking line 103 to another network node; and 2) retrieves STS-1 signals from frames received from another network node on an inbound networking line 102.
In the case of outbound transmission, other portions of the framer's networking system 110 individually provide each STS-1 signal carried by the outbound network line 103 to the framer 101. For example, a first STS-1 signal is presented to the framer at input 1071, a second STS-1 signal is presented to the framer at input 1072, etc. Consequently, for example, the framer 101 maps on outbound networking line 103: the STS-1 signal received at input 1071, across SPE positions 1111, 1121, 1131; the STS-1 signal received at input 1072 across SPE positions 1112, 1122, 1132, etc.
Correspondingly, in the case of inbound transmission, each STS-1 signal carried by the inbound network line 102 is individually presented by the framer 101 to higher layers of the framer's networking node 110. For example, a first STS-1 signal mapped on SPE positions 1111, 1121, 1131 is presented on framer output 1061, a second STS-1 signal mapped on SPE positions 1112, 1122, 1132 is presented on framer output 1062, etc. The individual outbound STS-1 signals may be collectively referred to as outbound STS-1 signals 105. Similarly, the individual inbound STS-1 signals may be collectively referred to as inbound STS-1 signals 104.
Note that different types of framers may exist. In one respect, the granularity of the inbound and outbound signals 104, 105 may vary. For example, with respect to SONET framers, each of the individual signals that collectively form the inbound and outbound signals 104, 105 may be comprised of a signal that consumes less bandwidth than an STS-1 signal (e.g., down to a 64 kbps signal) or more bandwidth than an STS-1 signal (e.g., each input signal may correspond to a group of STS-1 signals such as an STS-3 rate signal or an STS-12 rate signal, or higher). In another respect, different framing formats may be applied (e.g., SDH).